GB830141A - Improvements in instruments for testing vision - Google Patents

Abstract

830,141. Sight-testing apparatus. ASHER, H. M. F. May 3, 1957 [Feb. 3, 1956], No. 3417/56. Class 97(1) An instrument for testing and exercising vision comprises, for each eye, a light source for projecting a picture on a transparency on to a mirror and thence the eye of the patient through a lens system including a pair of circular cylindrical lenses; the component parts of the apparatus being adjustable for horizontal and vertical squint, to alloy for strength of spherical corrections and for astigmatic corrections in both strength and axis. As shown two cylindrical housings 1 contain light bulbs 2 which illuminate lantern slides 3 on which are represented letters of differing sizes. Above the slide is a suitably mounted convex lens 4 and a halfsilvered mirror 5 tilted at 45 degrees to the vertical. Two circular cylindrical lenses 6 and 7 of equal strength but opposite sign are arranged coaxially so that light from the lamp 2 reflected by the mirrors 5 will pass through them. Means are provided for rotating the lenses 6 and 7 in opposite directions, and additional means for rotating them simultaneously in the same direction. The housings 1 are adjustable for interocular distance, and also angularly adjustable about the pivots together with the rest of the optical system for each eye to allow for horizontal squint; tilting of the mirrors 5 about a horizontal axis allows for vertical squint. Motion of the lenses 6 and 7 in the sense indicated by D<SP>1</SP>, D allows for astigmatic corrections and vertical movement of the slides 3 allows for strength of spherical correction. The various motions may be provided with scales to indicate the correction to be applied. In use, the optician adjusts the controls until the patient sees clearly the charts on the slides 3, all the components are then swung out of the way so that the patient views an ordinary wall chart through lenses 6 and 7 only, the correcting glasses indicated by the test are then inserted in front of the eyes so that the wall chart is seen clearly as a check of the apparatus.